From an article at Publisher's Weekly:
"Cashore is currently working on a third book in the series, one that follows the story of Bitterblue, a character introduced in Graceling. Dawson is aiming for a 2011 release."
There were other words in the article, about the publication of Fire (a nice story about publishers playing nicely together), but the words I quoted are obviously of greatest importance. 2011 is less than 17 months away.
And actually, I still have Fire to look forward to...